Composite Spectrum Film-Thickness Sensing During CMP Polishing
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Solution Overview
Problem
Existing film-thickness measurement techniques in semiconductor manufacturing are inaccurate due to the absorption of light by polishing liquid and debris, limiting the wavelength range for optical measurement and affecting the accuracy of film thickness determination.
Innovation Solution
A film-thickness measuring apparatus and method that utilizes a liquid-seal sensor with a liquid flow passage and a transparent-window sensor, each with a different wavelength range, to extend the spectrum of reflected light and accurately measure film thickness by combining spectra from both sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transparent window or water flow is used to prevent polishing liquid contact with the sensor head, then the optical path is protected and measurement reliability is improved, but the wavelength range for light transmission is limited due to absorption by water and resin
Solution Approach 1:
The patent combines multiple sensor heads with different transparent window materials (e.g., quartz, sapphire, resin) into a single measurement system. Each material is optimized for specific wavelength ranges, and their measurements are integrated to achieve comprehensive film thickness measurement across a broad spectrum, resolving the contradiction between protection reliability and wavelength versatility.
Solution Approach 2:
The sensor head assembly is designed with multi-functionality by incorporating multiple transparent windows suitable for different wavelength ranges. This universal design allows the same sensor head structure to measure various film types (organic, inorganic, metal, dielectric) by selecting appropriate window materials, thus achieving both reliable protection and broad adaptability.
2Productivity
If polishing liquid and debris are present on the polishing pad, then polishing function is maintained, but light absorption increases and measurement precision deteriorates
Solution Approach 1:
The patent introduces a liquid seal (water flow) as an intermediary between the polishing liquid environment and the sensor head. This intermediary layer prevents direct contact between polishing debris and the sensor while allowing optical transmission, thus maintaining both polishing productivity and measurement precision simultaneously.
3Device complexity
If a single sensor head with fixed transparent window material is used, then device complexity is reduced, but measurement precision for different film types deteriorates due to limited wavelength range
Solution Approach 1:
The patent implements a dynamic sensor selection mechanism where the system automatically selects or switches between multiple sensor heads with different transparent window materials based on the film type being measured. This dynamic adaptation allows precise measurement of various film types (organic, inorganic, metal, dielectric) without requiring manual intervention, balancing device complexity with measurement precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method and apparatus enable accurate film thickness measurement across a wider wavelength range, allowing for precise determination of film thickness during polishing by alternating between sensors to compensate for light absorption issues.
Implementation Method 1
directing light to the workpiece from a liquid-seal sensor and a transparent-window sensor disposed in the polishing table and receiving reflected light from the workpiece by the liquid-seal sensor and the transparent-window sensor
Implementation Method 2
the liquid-seal sensor has a liquid flow passage through which liquid flows
Implementation Method 3
the transparent-window sensor has a second optical sensor head, and a transparent window arranged above the second optical sensor head
Implementation Method 4
determining a film thickness of the workpiece based on a spectrum of the reflected light from the workpiece
Data Source
AI summary
A film-thickness measuring method capable of substantially extending a wavelength range of a spectrum of reflected light from a workpiece, and accurately measuring a film thickness is disclosed. The film-thickness measuring method includes: pressing a workpiece against a polishing pad, while rotating a polishing table that supports the polishing pad, to polish the workpiece; during the polishing of the workpiece, directing light to the workpiece from a liquid-seal sensor and a transparent-window sensor disposed in the polishing table and receiving reflected light from the workpiece by the liquid-seal sensor and the transparent-window sensor; and determining a film thickness of the workpiece based on a spectrum of the reflected light from the workpiece.